doc: improve doc Http2Session:Timeout

Add line in doc/http2.md for 'timeout' event which tell readers
that 'timeout' event doesn't except any arguments.

Refs: nodejs/help#877
PR-URL: #30161
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/http2.md

@@ -311,6 +311,7 @@ added: v8.4.0
 After the `http2session.setTimeout()` method is used to set the timeout period
 for this `Http2Session`, the `'timeout'` event is emitted if there is no
 activity on the `Http2Session` after the configured number of milliseconds.
+Its listener does not expect any arguments.
 
 ```js
 session.setTimeout(2000);